Human blood or derivatives thereof is essentially universally administered to patients to treat anemia and/or blood loss when undergoing medical treatment (within surgical theaters, emergency rooms, hospital wards, and intensive care units). This blood generally is stored prior to any use in sterile polymeric receptacles or bags at about 4.degree. C. Typically, blood and other fluids are administered through what may be a labyrinth of tubing, filters, access ports, and valving devices to the recipient, transporting of the fluids being carried out by hydrostatic pressure as developed by an elevation of the receptacle above the patient or by use of an infusion device which applies external pressure to the blood bag. The rate of administration of blood varies with the circumstances, patients undergoing general medical services on a ward or the like receiving blood at relatively slower rates, while the administration of blood units during surgery often being carried at relatively accelerated rates. In the latter surgical theaters, several units of blood may be administered at these enhanced rates. Thus, a rapid transfusion of relatively larger amounts of cold stored blood would, without correction to normal body temperatures, cause a decrease in the body temperature of the recipient. For example, a recipient weighing about 100 pounds would experience a body temperature drop of as much as 0.5.degree. C. upon receiving a unit of blood at storage temperature. Where such a transfusion evoked hypothermia is experienced by a patient, various complications may ensue including a decrease in cardiac output, arrhythmias (and a temporary increase in serum potassium concentration). In this regard, see Anesthesia (Second Edition), edited by Ronald D. Miller, M.D., p. 1346, Churchill Livingstone, N.Y., 1981.
To avoid these hypothermic effects, practitioners commonly employ blood warming devices which are located (within the surgical theater) and the above-noted areas. These devices, which range from somewhat primitive warm-water baths referred to as Hemokinetotherm units to current "dry heat" warmers, serve to return blood or other fluids to a temperature of about 35.degree. C.-40.degree. C. in a manner non-destructive to proteins and blood cells like retained within the fluid media.
When blood at stored temperatures is rapidly warmed toward infusion temperatures by the above devices, there occurs a change in solubility characteristics of the gases which are entrained within the fluid, (particularly with respect to blood). Gas or "air" bubbles thus are formed, which, without some form of intervention, will be infused into the patient along with the administered blood. Any infusion of a large quantity of such gas or air may cause obstruction of the outflow tract of the right ventricle followed by reduction of pulmonary blood flow, and circulatory collapse. Generally, the latter condition is referred to as an air embolism which is the passage of air from the vein through the right side of the heart and the lungs, which causes pulmonary hypertension (increased pulmonary artery blood pressure) and impaired oxygen and carbon dioxide exchange across the lungs. A large air embolus can be fatal. Furthermore, fibrin may be formed on the blood-air interface of the right ventricle and then be deposited in the smaller branches of the pulmonary artery. Significant decreases in circulating platelets have been observed to be caused by air embolism. In the case of a small quantity of infused gas-air, the resultant bubbles will be trapped in the pulmonary arterial branches. Platelets may aggregate on the gas-blood interface off pulmonary arterial vessels. The passage of such bubbles also may cause pressure damage to endothelial cells in the pulmonary vaculature, resulting in deposits of fibrin on the walls of the vessel. In the above regard, see Mashimo, "Rapid Warming of Stored Blood Causes Formation of Bubbles in the Intravenous Tubing", Anesthesia and Analgesia, Vol. 59, No. 7, July, 1980, pp 512-513.
To avoid the above gaseous infusions of warmed blood and other intravenous fluids, practitioners now employ a cylindrical air trap within the labyrinth of distributing disposable tubing leading to the infusion point to the patient but downstream of the blood warming device. The air trap is quite simple being provided as a cylinder within which both air and blood collect, the blood being observed during an operation to drip into the chamber which, ideally, will contain about 1/2 fluid and 1/2 entrapped air or gas. By so arranging the trap such that the dripping is observable, the practitioner may be assured that blood flow is underway under the noted hydrostatic pressure. However, during the course of surgery, in many instances the amount of air-gases trapped may be in excess of the volumetric capacity of the air trap. When this occurs, the assigned personnel in surgery undertake a somewhat awkward and involved procedure in bleeding or removing air from the trap. The protocol requires that the trap be inverted with respect to its vertical sense, a syringe then is injected in a downstream port, the resultant flowing air bubble is observed as it progresses through the tubing toward the patient and is removed by hand through the syringe and needle arrangement as it reaches the air removal port. This protocal has lead to undesired incidents within the surgical theater, often results in an unwanted excursion of blood into the theater and generally represents an unsatisfactory condition.